First make sure your avatar fits within the correct size:
its width can be no greater than 150 pixels, the height no greater than 200 pixels, and the file size no more than 88 KB
Upload it on a free image-storing site such as http://www.imageshack.us or http://www.photobucket.com
Once uploaded on that site, you need to copy the url to the picture (in pictureproperties) (should give a link to the picture on a white page)
Then you have to follow the link to your profile in the menubar (tab-bar) (wood-design) just under the header of this page (starting with "Home" - "Forums" - "Library" ... to ... "My profile" - "Log out"
Go to "my profile" and scroll down to Avatar-control board...
There's a white bar to paste the link to the picture.
Don't forget to confirm your mail-address in your profile before saving.
Then all should be fine
If it doesn't work, feel free to mail me the picture and I'll arrange it for you
How big was it? Did it activate scrolling? Halve the text space? Could have been worse. When I last tried my previous avatar it was small on my screen... half a foot on everyone else's. 